Experimental Investigation on Optimization of Distorted Spot Shape in High-Average-Power Ho:YAG Laser Amplifier

A high-power Ho:YAG amplifier with in-band Tm:YLF laser pumping was established, reaching an output power of 221 W under 300 W pump power, corresponding to extraction efficiency of approximately 54%. However, pronounced degradation of beam profile occurred when further increasing the output power. The internal condition of the crystal, involving photo-elastic effect and inhomogeneous temperature distribution, would be more complex and severe when further amplifying power even in low-quantum-defect systems, which led to beam shape distortion. By spot size matching and divergence control, a near-Gaussian beam profile was successfully restored without drastic decrease in output power. In this study, the spot degradation was effectively suppressed while maintaining high average output power, not only advancing the design of in-band-pumped amplifiers but also providing a reference for other solid-state laser systems.